Summary Data
Across the twelve hospitals,
6,633 DAP values were harvested from the NIMIS database and transcribed into SPSS. Analysis included:
- Identification of median value for each projection and age group across the 12 clinical sites
- Identification of 75th centile of ranked median values.
- Range from highest to lowest median value
- Interquartile range
- Ratio maximum to minimum
- Ratio third to first quartile
Dap Dose Distributions
Ranked histograms with the 75th centile indicated were constructed for each projection by age group to visually feedback the results to the participating hospitals. Fig. 1 is an example,
depicting ranked median DAP values and 75th centile DRL value for chest projections in the age group 1-<5 years.
Considerable variations in median DAP dose between hospitals were demonstrated.
Across all hospitals,
minimum: maximum ratio of median DAP values ranged from 2.79 (for lateral lumbar spines in the 10<16 age group) to 15.46 (for AP pelvis in the 5<10 age group ( Table 1 ,
Table 2 ,
Table 3,
Table 4,
Table 5,
Table 6,
Table 7). This level of variation suggests immense potential for dose optimisation.
However the minimum to maximum ratio is extreme,
and advice suggests that greater attention should be given to the interquartile range,
since it is in this interval that the majority of practice will fit [5].
Overall the first to third quartile ratio ranged from 1.38 (for AP/PA Chest in the <1 age group) to 2.93 (for AP cervical spine in the 10<16 age group).
Since it excludes extremely high and low DAP data,
the interquartile ratio varies much less than the maximum: minimum ratio of median DAP doses.
However,
variations in median dose of between 1.3 and nearly three times between hospitals is still considerable and potential reasons must be explored.
Filtration:
Additional beam filtration removes low energy x-rays,
in turn increasing beam energy at a constant kVp [8].
This is recognised in literature to contribute to reducing entrance surface dose to the patient [9].
The hospital which has 81% of the lowest median DAP doses operates with the highest total tube filtration in the surveyed sites,
at 3.2mm Al equivalent,
and it is the only hospital to apply additional copper filtration of 0.1mm.
Proposed Diagnostic Reference Levels:
The 75th centile value of ranked median DAP values gathered in the current study are summarised in Table 8 and are proposed as age based DRLs for chest,
abdomen,
pelvis,
lumbar spine and cervical spine examinations.
NIMIS could not overcome data deficiencies for paediatric spine in younger age categories as spine is infrequently performed on young children.